1. Field of the Invention
The present invention relates generally to a two directional pressure relief assembly for use in a fluid transportation system, and in particular to a method and apparatus for providing a safety pressure relief device in either of two directions wherein means for alternatively weakening and strengthening are applied to a rupture disc. The pressure relief assembly includes means for mounting the rupture disc in such manner that the strengthening element of the disc is rendered additional support. The pressure relief assembly provides for resistance against bursting from very high fluid pressure in a first direction, while facilitating bursting from a much lower fluid pressure in a second direction.
2. Discussion of the Prior Art
It is known to provide a two directional pressure relief assembly for use in some fluid pressure environments. For example, a two directional pressure relief assembly may be used in a fluid reactor system, such as a chemical reactor system or the like. In such a situation, it is usually necessary to provide a safety device coupled to the reactor vessel to prevent a critical condition from occurring in the reactor vessel. The critical condition usually encountered in such an environment is an abnormal overpressure within the reactor vessel, with the safety device operable to relieve the overpressure to prevent catastrophic failure.
In the circumstances above described, it has been common practice to use a conventional single rupture disc designed to burst at a predetermined pressure. It was appreciated, however, that in many reactor systems it is necessary not only to provide emergency relief to prevent an overpressure from occurring, but also to prevent an underpressure from occurring. The initial solution to the problem presented by an environment presenting both overpressures and underpressures was to provide two conventional single rupture disc assemblies, one such assembly operable in each pressure situation. From this evolved a single assembly having two rupture discs mounted in the relief passageway connected to the reactor vessel.
Existing bidirectional relief systems as described above operate within a fairly narrow range of overpressures and underpressures. In fluid transportation systems, however, there has been a need for a bidirectional relief system capable of operating in a much wider range of pressures. In fluid transportation environments, such as may be utilized to transport a slurry of water and some particulate matter, such as coal or other ore, the concern to be addressed is the situation presented by the failure of one high pressure pump in a series of such pumps. It is common to provide a pressure relief circuit in connection with each pump in a fluid transportation system, such as will allow continuous forward flowing of the fluid being transported around the failed pump. These relief circuits are preferably designed so that there is one relief passageway upstream of each pump connected to a second relief passageway downstream of each pump, with a rupture disc disposed across the bore of each relief passageway. Each such rupture disc must be capable of withstanding the high backpressure normally present in the fluid transportation system while all pumps are operating. Should a pump fail, however, the upstream rupture disc is naturally designed to burst at a predetermined backpressure above the normal magnitude, so as to allow the fluid to enter the safety circuit, thus preventing damage to upstream pumps that continue to function. It is of course desirable that the rupture disc at the relief passageway downstream of the failed pump be designed to rupture at a much lower forward pressure, so that there is no delay in routing the fluid material back into the main fluid passageway after the upstream rupture disc has given way. Thus, the need has existed for a bidirectional relief system capable of withstanding very high backpressure, but also capable of rupturing at a significantly lower forward pressure.
As noted above, existing bidirectional relief systems operate in a relatively narrow range of overpressure and underpressure in fluid reactor systems. In a fluid transportation system as above described, however, the normal backpressure may be as much as 2200 psi. Nevertheless, in such an application, it is very desirable that the downstream disc in a safety by-pass loop be adapted to burst at a much lower forward pressure, on the order of 1000 psi. The purpose of this, of course, is to allow the fluid to flow freely as quickly as possible before damage occurs to upstream pumps.
Presently existing bidirectional pressure relief assemblies have further disadvantages. Such assemblies normally utilize two rupture discs with a sealing membrane disposed therebetween. This configuration is expensive to design and manufacture, particularly when considered in comparison to costs associated with an assembly having only a single rupture disc, such as is provided by the present invention.